1. Field of the Invention
The present invention relates to a method of attaching a sensor to a pickup head for reading data recorded on an optical disk such as a CD or a DVD, as well as a pickup head with the sensor attached thereto by that method.
2. Description of the Related Art
Conventionally, a pickup head is known as a device for reading data recorded on an optical disk such as a CD or a DVD. As is known, the pickup head is so arranged that data recorded on the optical disk is read by applying light emitted from a light source (laser diode (LD)) to a data recorded surface of the optical disk and detecting the reflected light by a light receiving element (photodiode (PD)).
The light receiving element is attached such that the center of its light receiving surface and the focal point of a focusing lens for focusing the reflected light from the optical disk are aligned with each other. A general pickup head is not provided with an adjusting mechanism for adjusting the position of the light receiving element attached to a main body. The reason is that the provision of the adjusting mechanism causes the problems of the main body of the pickup head becoming large in size and the higher cost.
Accordingly, in the general pickup head, when the light receiving element is attached to the main body of the pickup head, the light receiving element is fixed to the main body with an adhesive agent in a state in which the center of the light receiving surface and the focal position are aligned with each other.
Techniques for fixing an optical part to a main body with an adhesive agent are disclosed in, for example, JP-A-62-61033, JP-A-60-69611, and JP-A-63-223702.
However, the following problems have been encountered in a case where the light receiving element is fixed to the main body with an adhesive agent whose tensile force occurring at the time of curing is small (hereafter, this adhesive agent will be referred to as a soft adhesive agent).
The soft adhesive agent after curing undergoes large expansion and contraction in accordance with the change in the ambient temperature, so that the position where the light receiving element is attached is likely to change. For this reason, there has been a problem in that the pickup head with the light receiving element attached to the main body with the soft adhesive agent does not excel in the reliability with respect to the change in the ambient temperature.
On the other hand, in a case where the light receiving element is fixed to the main body with an adhesive agent whose tensile force occurring at the time of curing is greater than that of the aforementioned soft adhesive agent (hereafter, this adhesive agent will be referred to as a hard adhesive agent), the hard adhesive agent after curing undergoes small expansion and contraction in accordance with the change in the ambient temperature, so that it is possible to sufficiently ensure the reliability with respect to the temperature change. However, since the tensile force occurring at the time of curing is large, there has been a problem in that the position of the light receiving element changes at the time of curing.
Thus the soft adhesive agent has an advantage in that the positional offset of the light receiving element is small at the time of curing (attachment), but its reliability with respect to the change in the ambient temperature is low, whereas the hard adhesive agent has an advantage in that high reliability can be obtained with respect to the change in the ambient temperature, but the positional offset of the light receiving element is large at the time of curing (attachment).